1. Field of the Invention
The present invention relates to a stroke determination unit, and to a method of measuring stroke in a 4-cycle internal combustion engine. More particularly, the present invention relates to a stroke determination unit and method, suitable for determining stroke in a multiple cylinder 4-cycle engine.
2. Description of the Background Art
In a conventional 4-cycle engine that has adopted an electronic fuel injection unit, stroke determination may be performed based on both the phase of an engine camshaft and the phase of a crankshaft. In Japanese Patent Laid-open no. Hei. 10-227252, a stroke determination unit is proposed that does not detect the phase of a camshaft, but instead, for a particular crankshaft phase, compares intake pressure detected at a current time and intake pressure detected at a prior period, and carries out stroke determination according to a magnitude relationship of the two. In this way, since it is not necessary to provide a sensor for detecting the camshaft phase inside a cylinder head of the engine, it is possible to make the engine smaller and lighter in weight.
However, with the technology disclosed in Japanese Patent Laid-open no. Hei. 10-227252 described above, stroke determination takes a long time to effect, because stroke determination is carried out based on a magnitude relationship of measured intake pressures obtained using an intake pressure sensor, taking a magnitude relationship for all intake pressures into consideration, from a low-speed region of an internal combustion engine to a high-speed region. Also, since the comparison of magnitude values is made for a particular point, it is difficult to improve noise suppression with respect to the influence of interference, such as noise on an electrical system.